The used EHA valve you purchased
could be defective. They do go bad with age. As others have stated, it does sound like your mixture is needing adjustment. I know how you feel with the so called "specialists". If you read that book cover to cover I bet you'll show them. Below is the link for the book from Amazon.
http://www.amazon.ca/Bosch-Fuel-Injection-Engine-Management/dp/0837603005/ref=sr_1_1?ie=UTF8&s=books&qid=1293775377&sr=8-1-spell